A technique has been proposed in which a rectifier circuit is fabricated by combining a silicon Schottky barrier diode and a normally-on type GaN-HEMT (hereinafter referred to simply as HEMT). This technique makes it possible to produce a rectifier circuit having shorter reverse recovery time and higher voltage resistance than a general silicon PIN (P-Intrinsic-N) diode.
According to this technique, however, under a reverse bias mode, reverse leakage current flows through the Schottky barrier diode. The HEMT operates in a weak ON state, and thus leakage current flows through the HEMT while high voltage is applied between the drain and source of the HEMT. Accordingly, when the leakage current flowing through the Schottky barrier diode is high, the HEMT is operated beyond its safe operating area (SOA: Safe Operating Area), which leads to a breakdown of the HEMT.
Further, when the above rectifier circuit is used for AC operation or dynamic operation, at the timing of switching the rectifier circuit from a forward bias mode to a reverse bias mode, current for charging the junction capacitance of the Schottky barrier diode also flows between the drain and source of the HEMT. At this time, the HEMT is operated beyond its safe operating area since high voltage is applied between the drain and source thereof, which also leads to the breakdown of the HEMT.
When a Schottky barrier diode having low reverse leakage current is used in order to solve these problems, voltage applied to the Schottky barrier diode becomes excessively high and the Schottky barrier diode may possibly be broken down.